Stud driver attachment



June 12, 1962 J. F. HELDERMAN 3,038,159

' sTuD DRIVER ATTACHMENT Filed Nov. 15, 1957 I20 /0/F' INVENTOR:

JAMES FRANKLIN HELDERMAN I0 7 ATTORPUQYS United States Patent 3,038,159 STUD DRIVER ATTACHMENT James Franklin Helderman, Charlotte, N.C., assignor to Olin Mathieson Chemical Corporation, East Alton, 11L, a corporation of Virginia Filed Nov. 13, 1957, Ser. No. 696,214 8 Claims. (Cl. 1-445) This invention relates to a tool for projecting fasteners such as studs, bolts, and the like into frangible material such as concrete or similar substances which spall readily.

In the art of stud driving with explosive actuated tools, it is frequently necessary to securely anchor bolts, piping, electrical conduit, drop ceilings, and various other structural members into supporting structures of concrete or masonry and a very serious problem arises whenever such concrete cracks and shatters readily so as to produce a large rather than a small crater and thereby spoils the fastening installation where a neat appearance is an important factor in determining the success of the installation. Such spalling not only mars the surface but also is likely to weaken the bond between the impaled fastener and the concrete mass into which the fastener was projected. One rather successful method heretofore used to cope with spalling involves use of a rather large and heavy disk in direct contact with the concrete wall structure and of imperforate construction until the point of the fastener hits and penetrates the disk which as a result is thrust against the surface with sufficient pressure to hold the spall particles in place. Unless the disk is quite thick, it is likely to be ineffective. At any rate, its use has the disadvantage of requiring a heavier explosive cartridge load and one more part to be handled with each shot.

In these installations in concrete, the stress, shock and compression wave reflection conditions are such that some spalling is inevitable, but it is not the presence of a mere fracture line which is so objectionable, but the fact that large or many small pieces of concrete fall away over a considerable area of cratering surrounding the fastener, which otherwise may be driven adequately for the purpose.

Therefore, an object of this invention is to provide an improved tool attachment for explosive actuated stud driving devices giving improved spall minimizing or preventing characteristics to such tools. At any rate, one object is to provide an improvement in the explosive driver art which minimizes the cratering in concrete to no more than a small crater directly surrounding the area of penetration. Another object is to provide a spall minimizing device of relatively simple and economical construction for easy attachment and removal from explosively operated stud driving tools. These and other objects will become more apparent from the description of a specific embodiment when taken together with the accompanying drawing wherein:

FIG. 1 is an elevational view, partly broken away and in cross section, showing a preferred embodiment of the attachment installed on a typical preferred type of tool;

FIG. 2 is a view taken from the front end of the tool of FIG. 1, showing the face of the attachment; and

FIG. 3 is a semi-diagrammatic cross sectional view of a typical installation with a superposed grid system calibrated in terms of units equal to the diameter of the 3,038,159 Patented June 12, 1&62

be very effective in resisting and neutralizing the tendency of concrete to fracture under the impact of a projected fastener and spall in an area extensively surrounding the driven fastener. In any event, its construction provides for confinement of the spall to a small area immediately adjacent the driven fastener.

The pad takes the form and construction of a block of heavy, fracture resistant material, and more specifically of sufficiently heavy metal, such as steel, mounted at the muzzle of the tool. A heavy rigid steel ring about Me inch in thickness and from about 3 to 6 /2 inches in diameter with an orifice for passage of the tool barrel has been found suitable for most installations. This pad is far more effective and is superior to a mere pressing with the muzzle of the barrel or an extension in the form of a foot member only slightly larger than the barrel muzzle.

A still further refinement of the present invention is the provision of one or more relief recesses immediately adjacent the line of projection of the fastener, i.e. at the barrel bore, and between the tool barrel bore and the pressure face of the pad. This recess may take the form of an enlarged bore opening coaxially positioned at the muzzle and/ or a coaxial annular recess near to but spaced from the barrel bore. Such a recess provides for controlled eruption with stress relief manifested as small hardly noticeable cratering immediately next the driven fastener shank thus further minimizing the likelihood of large unsightly cratering. These recesses decrease the likelihood of spall extending outside the coverage of the pressure equalizing plate.

Also contemplated is the application of pad pressure by diversion of part of the explosive propellent gas in a manner obtainable with certain types of stud driving tools. Such pressure augments the inertia effect in supporting the concrete surface against the shock and pressure waves. For a .22 or .25 caliber tool barrel, a diameter of 3% inches has been found adequate except for the most unusual types of concretes. For a heavier tool, such as one using a .38 caliber tool barrel, a pad of about the same or slightly greater thickness and of a diameter of from about 5 inches to about 6 inches is generally adequate. This pressure equalizing pad or shield is mounted preferably on a pad support in slidable relationship with respect to the barrel of the tool of a co -pending patent application hereinafter identified and illustrated in FIG- URE 1 for obtainment of the angle fire control characteristics of this type of tool which insures that the fastener will be projected desirably with substantially exact perpendicularity to the surface while the pad exerts the shock equalizing and spall minimizing pressure.

The pad of this invention thus mounted provides an inertia mass which with the aforesaid surface supporting areas works to minimize spalling. For a typical .22 caliber tool, a total pad weight of at least 2 pounds at the tool muzzle has been found effective and for a .38 caliber tool a total attachment weight of not more than about 3 /2 pounds suffices for the most difficult and unusual types of concrete.

Relief recesses contemplated are one or more of (1) an annular gap of about of an inch near but displaced from the muzzle and (2) a countersink at the muzzle such as a /2 inch diameter countersink for a /2 inch or .22 caliber barrel or a inch countersink for a .38 caliber tool barrel.

The specific embodiment of the invention illustrated in FIGS. 1 and 2 will be described in connection with a tool generally of the type disclosed in US. Patent No. 2,945,236 granted to Rowland J. Kopf et al. This tool is preferably used as modified by the attachment in accordance with one embodiment of this invention, but it will be understood that other explosive operated tools may be similarly modified in accordance with this invention.

The tool shown in FIG. 1 comprises a barrel 22 adapted to carry at its breech end an explosive charge which when set off, projects the fastener into the work surface of the supporting concrete structure 11. This barrel is slidably mounted in an outer barrel housing tube 54 which is part of the main barrel assembly 18 of the tool. The other main tool assembly is the breech assembly 19 which includes breech housing 20a and the pistol grip or handle 20 with a firing means in the form of a trigger 46. These two major assemblies of the tool, which are pivotly connected about a hinge pin or screw 61 carried in a bifurcated hinged bracket 52 mounted on the barrel housing tube 54 in such a manner that both assemblies 18 and 19 move together as a unit as the housing tube 54- is telescoped downwardly over the barrel 22 as the muzzle of the latter is thrust against the work surface 11, contain elements which provide a control precluding firing of the tool unless the barrel is approximately square with the work surface. The connection also includes hinge ring 58 which is a part of assembly 19 positioned between front assembly 18 and the firing and trigger mechanism housing 20a; and hinge pin 61 fits into a longitudinal slot in L-shaped extensions of the ends of the hinge ring 58 in such a manner that the barrel assembly 18 and breech assembly 19 can move both axially and pivotally with respect to each other in engaging and disengaging the assemblies for loading of the tool and ejection of spent cartridges. For details of the elements contained in the assemblies and their operation, reference should be made to the aforementioned patent application.

The tool modification comprises the attachment consisting of a pad 100 3% inches in diameter and weighing about one pound mounted by any suitable means such as by screws 101 on a guard plate 102 having a mounting tube 103. Plate 102 is fastened permanently to the front end of guard plate or mounting tube 103 which is adapted to be telescopically mounted on the .22 caliber barrel 22 at its muzzle end for sliding movement between barrel 22 and the outer housing tube 54. Plate 102 may be optionally provided with peripheral walls such as the four walls 104 to minimize the blast of the explosive gases and to help in aligning the tool. Plate 102 is of any shape, but for this embodiment advantageously takes the four-sided four-inch square shape shown in FIGURE 2.

Pad 100 is mounted as a unit with plate 102 and tube 103- and the whole unit which weighs about 2 pounds is mounted on the tool barrel and constrained between muzzle nut 110, which is screw threadedly attached to barrel 22, and the shield spring 111 which is a compression spring mounted between barrel 22 and attachment mounting tube 103 for biasing tube 103, its plate 102, and the pad 100 forwardly against the muzzle nut 110 in such a way as to give angle fire control as explained in the aforementioned patent application.

It will be noted that the attachment is characterized by first recess 120 in the muzzle nut 110 adjacent barrel bore 22A and a second recess 121 of annular shape providing a clearance of about of an inch between pad 100 and nut 110.

Also noteworthy are barrel ports 22B through which explosive gas is ejected into tube 103 to provide a forward thrust proportional to the amount of propellant used.

In accordance with this invention, the diameter of the shield or pad may vary from a minimum equal approximately to at least twice the minimum radius of spall to a maximum preferably only slightly exceeding twice the maximum radius of spall so as to avoid a shield construction so large as to interfere with satisfactory accomplishment of the driving operation. These relationships are better understood in connection vw'th the view of FIG- URE 3 of the drawing illustrating various fastener driving and spall conditions which are encountered. When a fastener 10 is driven into concrete 11 it should be driven to a penetration of from 6 to 8 fastener diameters ordinarily inasmuch as this has been found to be the depth of penetration for obtainment of the best grip between the fastener and the concrete. The maximum depth of spall under these conditions varies from about 2 to 3 fastener diameters. The radius of the spall area at which the out-cropping of the spall line 13 (FIGURE 1) is evident has been found to vary from about 6 to 8 fastener diameters, or approximately the depth of penetration. Consequently, the angle of spall varies from the rather flat angle shown at A in FIGURE 3 for a relatively hard material to the rather deep angle shown at B for a relatively soft material.

In accordance with these principles, an advantageous size of pressure equalizing pad is selected for each tool barrel bore. For a .22 or .25 caliber barrel bore 22A, for example, the diameter of the pad should be at least 3 inches for the majority of conditions encountered in concrete, but for very hard materials should be about 4 /2 inches in diameter. In practice, a disk of about 3% inches outer diameter has been found quite effective. For a .38 caliber tool barrel bore, for example, the smallest shield should have a diameter of about 4 /2 inches and the largest convenient shield a diameter of about 6 /2 inches. It stands to reason that where size and convenience is not involved, the pads may be even larger. With the aforementioned sizes, a pad thickness of about /2 inch or slightly more for a steel pad has been found to be effective for providing the necessary inertia needed for pressure equalization. In practice, a 3% inch plate when mounted on a shield plate and tube constitutes a weight of about 2 pounds. A 6 /2 inch pad provides a weight of not more than about 3- /2 pounds added at the tool barrel muzzle.

With these proportions and the concomitant weights, the amount of spalling is reduced so markedly as to practically eliminate any falling away of material and to minimize the fracture itself in many instances. At any rate, no more than a spall line and a slight amount of spalling is produced in those instances where previously the entire piece of concrete above the spall line was ordinarily ejected by the pressure and shock reflection waves generated in the concrete by the act of fastener penetration to leave a large unsightly crater containing the fastener. Fracturing, if any, is along the former spall line 13 approximately and usually within the confines of pad and spalling, if any, is confined to the region limited by spall line 14 located close to the shank of fastener 10.

By inertia weight is meant that mass expressed in terms of gravity weight, i.e. in pounds instead of slugs.

It will be understood that although the best results are obtained with the tool shield attachment of the present invention when gas pressure is applied to urge the relatively ponderous and broad pressure equalizing pad against the concrete surface and when at least one stress relieving recess is provided, improved results are obtainable relative to prior tools even when either or both features are omitted. It will be appreciated that the attachment can be readily installed and removed from the driving tool and that for sizes of tools other than those described herein, a tool design will vary the transverse expanse and the weight in accordance with this invention until satisfactory performance is obtained. It will also be appreciated that a washer may be implaced in recess and that the pressure pad 100 may be of split construction with hinged halves or may include a plurality of hinge fingers for coacting with parts of the fasteners such as a shouldered fastener.

Since other modifications and changes may occur to those skilled in the art, the foregoing is intended to illustrate the invention and not to limit its spirit and scope except as set forth in the appended claims.

What is claimed is:

1. In a stud driving tool having a barrel through the bore of which a fastening stud is adapted to be propelled by an explosive charge in the direction of the barrel axis substantially squarely into the work surface of a relatively frangible body such as concrete and the like, a substantially rigid pressure applying member mounted reciprocatably with respect to said barrel at the muzzle end of the barrel with a forward bias for presenting an inertia weight separate from said barrel and of not less than about two (2) pounds to said work surface sufiicient to effectively resist spalling, said member having a work surface contacting area extending outwardly from said axis circumferential-1y around said barrel by a radial expanse of not less than about from 6 to 8 stud diameters and suflicien-tly to contact at least the probable extreme limits of the surface outcroppings of lines of fracture of said body occasioned by driving of the stud.

2. The device of claim 1 including a circumferential relief recess surrounded by the area of the member adjacent the muzzle of the barrel.

3. The device of claim 1 wherein the member includes a transversely extending coaxial ring of steel not less than about /2 of an inch thick.

4. The device of claim 1 wherein the tool barrel has about a .22 caliber bore substantially centered on the member regularly extending about said barrel and wherein the transverse expanse of said member in any direction is from about 3 inches to about 4 /2 inches.

5. The device of claim 1 wherein the tool barrel has about a .38 caliber bore substantially centered on the member regularly extending about said barrel and wherein the transverse expanse of said member in any direction is from about 4 /2 inches to about 6 /2 inches.

6. The device of claim 1 wherein the member is a metal pad with minimum dimensions transverse to the barrel bore extending substantially regularly around the barrel within the range of from about 3 inches to about 6 /2 inches.

7. In a stud driving tool having a barrel through the bore of which a fastening stud is adapted to be propelled by an explosive charge into the work surface of a relatively frangible body such as concrete and the like, the combination comprising a forwardly extending housing tube, a rearwardly extending tube in substantially coaxial outwardly spaced relationship with respect to the tool barrel and mounted thereon for limited reciprocation, and a substantially rigid outwardly extending pressure applying member mounted adjacent the muzzle end of the barrel and having a frontal area for contacting the work surface extending outwardly from the barrel of the tool by a radial expanse of not less than about 6 to 8 stud diameter-s, said member being of sulficient inertia weight to effectively resist spalling and including a rigid pad supported upon said rearwardly extending tube for reciprocation of said pad about said muzzle end, said pad bearing tube being telescopically mounted between said barrel and said tool housing tube through its open frontal end, said barrel being ported adjacent its muzzle end into said pad tube, said pad including a thrust area opposite its work surface contacting frontal area for receiving part of the force of the gaseous products of the explosive charge escaping through said ports, thereby applying through said pad a holding pressure to the work surface for resisting the tendency of the surface to spall excessively around the barrel in an outward region beyond the driven stud, said member presenting an inertia Weight of not less than about 2 pounds to said work surface over the contacting area.

8. A powder charge actuated fastener driving tool comprising a housing, a barrel reciprocatably mounting said housing thereon and having a fastener ejecting axial bore and muzzle, means for preventing operation of the tool unless said barrel bore is approximately in perpendicularity with the work surface of a relatively frangible body into which the fastener is to be driven and a substantially rigid, forwardly biased, transversely extending pressure applying pad reciprocatably mounted relative to said barrel and housing for abutment with said surface when the muzzle of said barrel is abutted thereagainst in said perpendicular relationship, said pad having a substantially annular work surface contact area extending around said bore radially outwardly to an extremity of from about 1 /2 inches to about 3% inches, said area including at least one concentric annular pressure relief recess located adjacent said muzzle and remote from said extremity and presenting an inertia weight of not less than about from 2 pounds to about 3 /2 pounds to said surface in said area.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,569 Sopris Oct. 28, 1952 2,400,878 Dunn May 28, 1946 2,702,902 Portouw et a1 Mar. 1, 1955 2,771,607 Skumawitz Nov. 20, 1956 2,787,000 Smith et al Apr. 2, 1957 2,910,701 Temple et al Nov. 3, 1959 2,945,236 Kopf et a1 July 19, 1960 2,966,683 Schulz Jan. 3, 196 1 FOREIGN PATENTS 167,800 Australia June 6, 1956 1,123,658 France June 18, 1956 

